Lecture series on SES and capability-based security by Mark Miller

Axel Rauschmayer axel at rauschma.de
Fri Nov 4 20:38:59 PDT 2011

> I agree completely (see also my other email):
> - Never use objects as maps.
> - Introduce collection classes.
> - Try to make arrays fit into the collection framework.
> Great! But could you please post a pointer to that other email, or post a summary? Thanks. 

This is the original thread:

My understanding (using Allen’s terminology) is as follows (consult Allen’s email that started the thread for further details and a longer rationale).

We have to separate the data domain from the program domain:
- Arrays: [] is used to access both collection/array elements (data domain) and properties (program domain).
- Objects: [] is used mainly for properties, but also for collection element access when (ab)using objects as maps from strings to values.

1. New operator for the data domain: Introduce a new, separate operator .[] for accessing collection elements. Use it for all new collection types, implement it for arrays, too.  
2. Rededicate [] to be used for the data domain only: Default behavior remains as is, but can be overridden in collection classes (including arrays). Using [] for property access is deprecated, you must use methods such as Object.setOwnProperty() and Object.getProperty() to do so.

Addendum: edited quote from a recent email of mine:

> I think it’s better to rededicate [] to be a collection element accessor:
> - Introducing .[] would deprecate all existing array code and code that uses objects as maps.
> - Rededicating [] would only deprecate code that uses computed property names.
> It might make sense to have a "stricter mode" that turns off the default behavior of []:
> - It would thus force you to use methods such as (the yet to be defined) Object.setOwnProperty() and Object.getProperty() when you want to compute the name of a property.
> - Stricter mode could also restrict [] for arrays to just numbers, including negative numbers for accessing elements relative to the end of an array.

Dr. Axel Rauschmayer
axel at rauschma.de

home: rauschma.de
twitter: twitter.com/rauschma
blog: 2ality.com

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